The development of polyaniline and its derivatives in the field of conducting polymers has yielded materials that can be formed into, e.g., continuous fibers and surface coatings through solution processing in organic-solvents such as N-methylpyrrolidone. Films of polyaniline have been used in electrical devices and as corrosion resistant undercoatings. A major problem in processing polyaniline solutions is that the solutions tend to gel over periods of time ranging from several minutes to several hours. It has been suggested that this tendency of solutions of polyaniline in the emeraldine base form to gel is due to crosslinking of polymer chains. Such crosslinking has been generally attributed to formation of physical crystalline regions or to formation of chemically bonded regions through oxidative processes.
In U.S. Pat. No. 5,135,682, Cohen et al. describe stable solutions of polyaniline generally including from about 10 to 30 percent by weight of polyaniline in a solvent selected from the group of 1,4-diaminocyclohexane, 1,5-diazabicyclo[4.3.0]non-5-ene, and a mixture of N-methylpyrrolidone with either pyrrolidine or ammonia in an amount sufficient to dissolve the polyaniline.
Unfortunately, the solvents and additives of Cohen et al. are all either liquid or gaseous. In the application of coatings, minimization of volatile organic content (VOC) has become a major objective because of pollution concerns. Thus, one desire would be a solid additive that could stabilize polyaniline solutions and avoid any additional VOC.
It is an object of the present invention to provide stabilized solutions of polyaniline or derivatives of polyaniline, such solutions including selected stabilizing additives, preferably selected solid stabilizing additives.
It is a further object of the invention to provide a method for stabilizing solutions of polyaniline or derivatives of polyaniline by addition of selected stabilizing additives, preferably addition of selected solid stabilizing additives.